The present invention relates to a portable engine such as a compact 2-cycle engine with a cassette suitable for being mounted to a portable operating machine of which an operating attitude of which can be freely changed, for example, a brush cutter, and using a liquefied petroleum gas such as LPG and butane within a cassette gas bomb as a fuel therefor.
A compact 2-cycle engine using the LP gas (the LPG) as a fuel is light and compact, so that it is suitable for being mounted to an operating machine such as a brush cutter. The apparatus using this fuel gas has the features as follows.
That is, since the fuel is gas, in comparison with the case when gasoline is used for the fuel, there is less trouble in the fuel supply system due to corrosion in the piping system caused by the fuel since the combustion is better performed, less HC and CO contained in the exhaust gas is discharged. Further, since it is not necessary to produce a mixed fuel including gasoline and lubricating oil for combustion, the operator's hand does not become rough due to the used fuel, the peripheral portion does not become dirty and the danger due to the fuel is reduced. Further, since the igniting performance in the case of gas is better than the case of gasoline, starting can be performed at a lever position in the idling drive state, so that no choke is required. In addition to this, the rotational speed in the driven side at a time of starting is made low so as to be safe. Still further, since the fuel is sealed within the cassette type gas bomb, the fuel can be easily attached and detached so as to be better treated.
For example, there is provided an engine disclosed in Jpn. UM Appln. KOKOKU Publication No. 3-4774 as a compact 2-cycle engine using LP gas for a fuel. The suggested 2-cycle engine is provided with a detachable gas bomb 11, an automatic pressure adjusting apparatus APC reducing a high pressure gas in the gas bomb 11 so as to supply to a Venturi tube 9 communicating with a suction port of an engine body 1, a gas leakage prevention apparatus 12, a gas amount adjusting valve 13 and a lubricating oil pump apparatus 16, as shown in FIG. 5 of the present invention. Further, the automatic pressure adjusting apparatus APC including the gas leakage prevention apparatus 12 is disposed in such a manner as to be exposed to a discharge wind from a cooling wind outlet port 10a of a muffler 10 so as to promote gasification of the LPG.
The gas leakage prevention apparatus 12, the gas amount adjusting valve 13 and the lubricating oil pump apparatus 16 are respectively disposed downward of the automatic pressure adjusting apparatus APC after adjusting the gas pressure, and the gas leakage prevention apparatus 12 is integrally structured with the automatic pressure adjusting apparatus APC and shuts the gas in the gas flow passage in response to the pressure within a crank case 4 of the engine body 1. The gas amount adjusting valve 13 adjusts the amount of the gas flowing through the gas flow passage, and the lubricating oil pump apparatus 16 sucks the lubricating oil from a lubricating oil tank 15 so as to inject to the Venturi tube 9.
Further, the lubricating oil pump apparatus 16 is structured in such a manner as to respectively form a pulsation pressure chamber and a pump chamber on both sides of a pump diaphragm mounted to an inside portion of the lubricating oil pump apparatus 16 and connect the pulsation pressure chamber to the crank chamber, thereby using a pulsation pressure in the crank case 4 as a back pressure in the pump diaphragm so as to operate the pump by beating the diaphragm. Accordingly, the lubricating oil within the lubricating oil tank 15 is injected into the Venturi tube 9 so as to be atomized and thereafter is mixed with the gas flowing within the Venturi tube 9 so as to be supplied to the engine body 1.
However, in the compact 2-cycle engine using LP gas for the fuel, there is produced some problems to be solved. Accordingly, in the compact engine, as is representative of the case of being mounted to the brush cutter as mentioned above, since the attitude during operation is greatly changed, there is often required a case where the engine is operated in an inverted state. Further, in order to lighten the engine, it is necessary to increase the output per the unit weight of the engine and to essentially drive at a high rotational speed. Still further, it is necessary to form as compact a unit as possible.
On the contrary, in the compact 2-cycle engine using LP gas for the fuel, the lubrication system is made as a separate lubrication system as a matter of course, so that a lubricating oil pump mechanism is required. Further, a mechanism for gasifying the LP gas and adjusting the pressure is also required. However, when the lubricating oil pump mechanism and the fuel supply mechanism added, it is disadvantageous for making the engine compact and light. Further, it is necessary to make these mechanisms suitable for conditions such as great attitude change of the engine and high rotational speed.
For example, for a lubricating oil pump for a compact 2-cycle engine having a separate lubrication system, a diaphragm type lubricating oil pump is generally employed in many cases, as described in the above publication. However, since a pump of this kind has a deteriorated responsibility with respect to the pulsation pressure within the crank chamber of the engine at a time of high speed rotation, and it is difficult to increase the oil hydraulic pressure, there is a risk that the supply amount of the lubricating oil becomes insufficient at a time when the engine is driven at a high speed load.